Terms in this set (23)
Geiger counters are a detector with what Pros?
inexpensive, sensitive to low energy levels, light weight & reliable, easy for mobilization
Geiger counters are a detector with what Cons?
They have a large dead time, are inefficient at high energy photons, they have a very short useful life time comparatively to other detectors, they don't measure dose rate, exposure, or energy
How do Geiger Counters work?
Photons interact via photoelectric effect w/ cathode, liberating electrons. A massive electric field near the anode that pulls in electrons, which pick up speed and energy as they get closer, interacting with other electrons and creating ion pairs as they go, slowly causing an avalanche
Proportional Counters are a detector with what Pros?
Very short dead time, they find dose rate & output, they differentiate kinds of radiation, very sensitive (can detect a single ion pair)
Proportional Counters are a detector with what Cons?
effected by temperature, humidity and pressure
sensitive to voltage fluctuation
low efficiency for photons
How do Proportional Counters work?
they utilize a higher voltage and electric field than that of ionization regions and cause Townsend avalanches which causes a single ion pair (created by ionizing radiation) to multiply in the order of 10^2 - 10^4 before reaching the anode
Radiochromic film is a detector with what Pros?
self developing, waterproof, very high resolution, dose accuracy of 3-5 %, easily cut into shapes or sizes, tissue equivalent
Radiochromic film is a detector with what Cons?
One use only, heat sensitive, max dose between 3 -15 Gy depending
What was the first method to detect ionizing radiation?
Scintillation / Florescence
Scintillation ( Florescence ) is a detector with what Pros?
high light output, relatively inexpensive, very small dead times, detects gamma rays and x rays
Scintillation ( Florescence) is detector with what Cons?
sensitive to light leaks, sensitive to heat &temperature changes, absorb water and water vapor
Semi-Conductor is a detector with what Pros?
Solids interact with photons, sharper energy resolutions and have a low power consumption
Semi-Conductor is a detector with what Cons?
Some need liquid Nitrogen, they have a small W which means sensitive to light, Crystal structure is easily damaged
Ionization Counter is a detector device with what Pros?
Cheap, differentiates kinds of radiation, yields exposure rate directly, current is independent of voltage and has small dead times
Ionization Counter is a detector device with what Cons?
Needs amplification to measure cps, low sensitivity, sensitive to temperature, heat, & pressure, loud amplifier noise causes inaccurate count rates
What are the two modes of Ionization chambers?
Pulse or Current (integration)
What are the two gas Ionization chambers?
parallel Plate and Farmer
What type has a coaxial electrode configuration?
Farmers Ionization Chamber
Farmers Ionization chamber has a uniform field and a parallel plate ionization chamber has a non uniform field.
Farmers field is stronger towards the anode in the middle of the setup and weaker towards the cylindrical cathode. Whereas the field in a Parallel Plate Chamber is Uniform
In the ionization region, what is taking place to Ion pairs and what is the Voltage?
Voltage is much greater than initial voltage
almost all of the ion pairs are being collected before recombination takes place
emission of light by heat; storage of e- in traps in the forbidden zones of insulators; LiF TLD-100 most common
economical, small size, resusable, wide useful range, dose rate independent, good in vivo dosimeter, tissue eq.
loss of reading(single use), fragile, structural damage, fading of signal with time, spurious TL
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